This invention relates to printers, and, more particularly, to the ink delivery system for an inkjet printer.
Printers are used to print the output from computers and similar types of devices that generate information, onto a printing medium such as paper. The presently available types of printers use a variety of techniques to transfer ink to the printing medium in the desired pattern. Commonly available types of printers include impact printers, laser printers, and inkjet printers. An inkjet printer transfers ink to paper in the form of a fine stream or droplets from the source to the paper.
One popular type of inkjet printer is the thermal inkjet printer. In a typical thermal inkjet printer, a small volume of ink is contained within an ejection cavity in a print head that moves along a prescribed printing path. The ejection cavity has an electrical resistor in its wall. At a precisely timed point, an electrical current is passed through the resistor, causing the resistor to heat, in turn heating the ink immediately adjacent the resistor. Some of the heated ink is vaporized, expanding to drive a tiny droplet of ink out of the cavity to impact and deposit upon the paper.
The present invention deals with the manner in which ink is supplied to the print head. Numerous approaches have been utilized to provide ink to the print head. In one type of conventional inkjet printers, an ink supply is provided within a sack supported inside a container mounted upon the print head. The interior of the container is maintained at a pressure slightly below atmospheric pressure, so that the ink within the sack is also at a pressure slightly below atmospheric pressure. This reduced pressure is necessary to prevent the ink from leaking out of the print head in the absence of a heating pulse in the resistor.
Ink from the reservoir is drawn to the ejection cavity through a capillary. Exactly the right amount of ink to replace that ejected is drawn through the capillary, so that the ejection cavity is instantly refilled after a droplet is ejected. The sack reservoir system works well in many types of inkjet printers, and is the standard of the industry.
However, the conventional reservoir system has some disadvantages. Sometimes it is difficult to maintain the proper negative system pressure. The reservoir is mounted on the moving print head, so that the weight and cost of the print head, the mounts, and the traversing mechanism and its power supply are increased beyond what is otherwise necessary. Bubbles of air formed within the sack may be drawn into the capillary, resulting in interference with ink ejection by starving the ejector.
Another important concern with conventional inkjet printers is the buildup of heat in the print head. As each droplet is ejected from the print head, some of the heat used to vaporize the ink driving the droplet is retained within the print head. This heat can gradually build up, with the result that the change in temperature of the print head alters the ejection performance. That is, if the print head is operated at high speed and with the ejection of large amounts of ink, its temperature may become so high as to impair further operation. Heat buildup is one of the primary factors limiting the printing capacity, output quality, and speed of some inkjet printers.
There exists a need for an improved method of supplying ink to inkjet printers. The new approach would desirably avoid the problems encountered with the present ink supply system, and additionally would contribute to solving the heat buildup and bubble accumulation problems. The present invention fulfills this need, and further provides related advantages.